The invention concerns a process for triggering a passive safety device for vehicle occupants inside a vehicle where--by means of electric sensors that detect a critical vehicle condition, an evaluation circuit, and triggering agents for the safety device--an activation of these triggering agents is effected in relation to the acceleration signals supplied by the sensors.
Passive safety devices for motor vehicles, such, as, e.g., airbag systems, pretensioning systems, or roll-over bars, serve to protect vehicle passengers from injuries in the event of a vehicle collision (crash) occurring.
Known triggering processes of such safety devices will feed the acceleration signals, which are generated either by a single or even by two acceleration sensors, into an integration device in order to compare then the integration value with a crash threshold, and subsequently trigger the passive safety device if necessary.
Before acceleration signals are integrated these will usually be amplified, filtered, and fed to an unsymmetrical limiter as known from DE 38 16 587 A1. By means of a differential circuit a reference value will be subtracted from any signal generated in this way; and only then will it be fed into an integrator. Further processing of the integrated acceleration signal is effected by means of analog technology.
In addition to the analog processing of acceleration signals, their digital processing is also known, for example from DE 37 17 427. There, the acceleration signals of two sensors will be fed into a sample and hold circuit after amplification and filtering; the output signals of such a sample and hold circuit are digitized by means of a post-connected A/D converter. These digitized sensor signals are then processed by a microprocessor.
Such digital processing is also known from DE 30 01 780 C2 where the acceleration signals are converted by means of an 8 bit analog/digital converter and processed by an 8 bit processor.
The cost and effort entailed by such 8 bit processing is not inconsiderable as it involves a very high memory storage and calculation requirement.
Finally, from DE 41 17 811 C2, a process for evaluating sensor signals is known where these signals are first digitized as acceleration signals after analog processing. These digitized acceleration signals will be entered over a predefined time period in succeeding time intervals and stored within a shift register. The difference calculated from the current acceleration value and the previous acceleration value lying in the past by the said predefined time period will then be fed into an integrator in order to calculate the differential velocity whose value is used as a trigger criterion. However, in order to implement storage and difference calculation an 8 bit resolution will be required here also.